The present invention relates to a LSI test circuit and, more particularly, to a LSI circuit for checking connection between external connection pins of a LSI, mounted on a printed board, and a wiring pattern of the printed board.
After a LSI is mounted on a printed board, the following conventional methods have been used to check whether a wiring pattern on the board is electrically connected to the external connection pins of the LSI without defects: a method of checking connection by visual inspection; a method of checking connection by forming through paths in a LSI from input pins to an output pin and testing whether a pattern given to the input pins appears at the output pin without changes; and a method of checking connection by putting a probe, having one-to-one correspondence with a net, on a surface, of a board, opposite to its LSI-mounting surface, applying a test pattern to input pins, and checking a pattern appearing at an output pin (in-circuit test).
Of the above-mentioned conventional methods of checking soldering, in the checking method based on visual inspection, oversight and misreading tend to occur, and a large number of steps are required to check current LSIs each having 500 pins or more. In the method of forming through paths, since a selector for switching a through path and an internal path is required at an output portion, the hardware amount is undesirably increased. In the in-circuit test method, as an internal circuit becomes more complicated with an increase in integration of a current LSI, it is difficult to identify a correlation between a test pattern given to certain input pins and a pattern appearing at an output pin. More specifically, if an improper output pattern is obtained, in order to determine whether it is caused by a defect in soldering of input/output pins or by a defect in the internal circuit, an enormous amount of test patterns are required, resulting in difficulty in analysis.